1. Field of the Invention
The present invention relates to a multicolor image forming apparatus which utilizes an electrophotographic process and, more particularly, to a multicolor image forming apparatus which uses a character font.
2. Description of the Prior Art
In a known image forming apparatus, character data is transferred in the form of code data, and the code data is converted to image data consisting of pixels of 1 to several bits to obtain a visible image.
Data to be referred to in this conversion is called a font. In order to convert the font into image data, special-purpose data conversion means is used.
The conventional image forming apparatus described above forms image data by utilizing a character font, and forms a black-and-white toner image on the basis of the image data. This apparatus cannot record a color character.
If a color character can be recorded in a corresponding color, the recorded character looks fine.
When a color character is recorded, if its density (gradation) can be controlled, a character can be recorded to have a density corresponding to a character color.
Various image forming apparatuses for forming a color image are known. Of these apparatuses, an apparatus described in U.S. Pat. No. 4,679,929 has a simple arrangement, and can achieve a high-speed operation and high image quality as features of the electrophotographic technique. The characteristic feature of this apparatus is formation of toner images color by color in layers on a photosensitive body (image forming body).
Color reproduction in this apparatus is performed by forming a plurality of kinds of toners in layers at an identical position on the photosensitive body or to be adjacent to each other. However, the way of forming image data of a character when a color image is formed by this apparatus is not described.
It is conventionally considered that when a color character is recorded, a black-and-white character font can be used.
However, when a recording apparatus according to an electrophotographic technique described above is used as a recording means, the following problems are posed.
Such a recording apparatus has a drum-like image forming body. After a toner image of a first color is formed on the image forming body, a toner image of a second color is formed on the toner image of the first color to overlap it in the next process. Such an image forming process is performed for all the color-separation images.
When all the image forming processes are completed, fixing and separation processes are performed, so that a color original is copied and recorded on a normal recording paper sheet.
When a recording unit for forming multicolor toner images in layers is used, the toner image of the first color has a different amount of attached toner from that of the toner image of the second color, thus impairing color reproduction characteristics, as will be described in detail later.
If font data can be selected according to a user's favor, this results in very convenience.
When yellow, magenta, and cyan toners are used, a green character is obtained by overlapping yellow and cyan toners on the image forming body.
When a multicolor toner image is formed by overlapping color toners, the overlying toner layer is not easily attached to the underlying toner layer, or a peripheral portion of a character is blurred, thus degrading color reproduction characteristics and recording quality, as will be described in detail later.